The present invention relates to a packaged semiconductor device and techniques for manufacturing same and in particular to techniques useful when applied to an LSI package having numerous pins or a small pin arrangement pitch such as a QFP (Quad Flat Package).
Dam bars are disposed in a lead frame used for fabricating an LSI package. A dam bar is a member disposed in an intermediate portion of each lead of the lead frame so as to couple leads adjacent to each other and has a function to prevent molten resin injected into a molding unit from flowing out to the exterior of the molding unit through spaces between different leads, when a semiconductor chip mounted on the lead frame is molded with resin. It has further a function to act as a supporting member for preventing deformation of the leads. The dam bars are cut away by means of a cutting tool such as a press, etc., after the semiconductor chip has been molded with resin.
However, recently, for lead frames used for fabricating LSI packages involving numerous pins, since an increase in the number of pins or leads and a decrease in the pin arrangement pitch are advanced rapidly, it becomes more and more difficult to cut the dam bars by means of a press.
Therefore, in lieu of a lead frame in which dam bars and leads are formed in one body from a metal plate, so-called tape dam techniques have been proposed (JP-A-58-28841, published on Feb. 19, 1983) in which a thin insulating tape is applied to a lead frame having no dam bars, and the tape is pressed between different leads in a resin molding operation to use the pressed parts of the insulating tape as dam bars. According to these tape dam techniques, since the tape is made of an insulating material, dam cut after the resin molding is unnecessary and thus it is possible to increase the number of pins or leads and to decrease the pin arrangement pitch.
Techniques similar to the tape dam techniques are disclosed also in U.S. Ser. No. 08/161,374 filed on Dec. 2, 1993 and U.S. Pat. No. 5,106,784 issued on Apr. 21, 1992.